lzma decoding consistently takes about 8mins on my N900, both on eMMC and SD card (class 6).
I believe the 5x longer decoding times some people observe are due to simulatenous flash access of other applications and/or swapping due to low memory.
You may see a similar effect on your desktop PC if you copy two very large file one after another vs. simulatenously.
I recommend to close all applications or better reboot before decompression.
ssh access might help but I don't think it is necessary.

I would be nice if you could vote for the promotion of lzma to extras
if you did not have any problems with the package
http://maemo.org/packages/package_in...4.43-14maemo4/